The present invention relates to a novel mixer and process for mixing at least two fluids. The mixer comprises a mixing chamber, at least two conduits to supply fluids in both tangential and radial directions into the chamber, and a mixing chamber outlet to discharge a stream of mixed fluids.
When mixing at least two fluids, the objective is to achieve a uniform distribution as rapidly as possible. It is advantageous to use the static mixers described by W. Ehrfeld, V. Hessel, H. Lxc3x6we in Microreactors, New Technology for Modern Chemistry, Wiley-VCH 2000, p. 41-85. Known static mixers achieve mixing times for liquids between several milliseconds and 1 second by generating alternate adjacent fluid layers of micrometer range thickness. The higher diffusion constants for gases provide even more rapid mixing. In contrast to dynamic mixers, where turbulent flow conditions prevail, the predetermined geometry of static mixers allows precise fixing of the fluid layer widths-and diffusion paths. As a result, a very close distribution of mixing times is achieved. This allows numerous possibilities for optimizing chemical reactions with regard to selectivity, yield, and even safety.
A further advantage of static mixers is a reduction in component size, allowing greater ease of integration with adjoining equipment, such as heat exchangers and reactors. Process optimization may also be enhanced due to forced interactions between two or more components within a confined space. Static mixers apply to forming not only liquid/liquid and gas/gas mixtures, but also liquid/liquid emulsions and liquid/gas dispersions. Static mixers have also found use in multiphase and phase-transfer reactions.
A static mixer operating using the principle of multilamination or fluid layering has, in one plane, a structure of intermingled channels of a width of about 25-40 microns (i.d., pp. 64-73). The channels divide two fluids to be mixed into a multiplicity of separate fluid streams, arranged to flow parallel and alternately in opposite directions. Adjacent fluid streams are removed vertically upward out of a horizontal plane and through a slot and are brought into contact with one another. Using structuring methods suitable for mass production, however, the channel geometries and therefore the fluid layer widths can be reduced to the submicron range to only a limited extent.
A further reduction in the size of fluid layers using the multilamination principle is achieved by so-called geometric focusing. A static mixer using this principle for reacting hazardous substances is described by T. M. Floyd et al. in Microreaction technology: industrial prospects; proceedings of the Third International Conference on Microreaction Technology/IMRET3, W. Ehrfeld, Springer 2000, pp. 171-179. Alternately adjacent channels for the two fluids to be mixed open outward in a semicircle, radially from the outside, into a chamber extending into a funnel shape and merging into a narrow, elongate channel. The layered fluid stream is combined in the chamber and then transferred to the narrow channel, so that the individual fluid layer width is reduced. Under these laminar flow conditions, mixing is purely diffusional. Therefore, mixing times in the millisecond range are achieved by reducing the fluid layer width to the submicron range. A drawback with this configuration is that the narrow channel must be sufficiently long to achieve full, intimate mixing. This requires a large structure and promotes relatively high pressure loss.
In contrast to these disclosures, the present invention provides a solution to the well-known problem of mixing at least two fluids rapidly and uniformly, while at the same time maintaining low pressure drop characteristics and an economical design.
The present invention is a mixing apparatus and method of mixing that overcome limitations of known mixing operations associated with high pressure drop and insufficient diffusion. Mixing is accomplished by injecting streams of individual fluids in both radial and tangential directions about a mixing chamber to provide an overall helical flow path. Although the invention may be used in a wide variety of applications, the invention is particularly suited for small-scale mixing operations, or micromixing.
In a first embodiment, the present invention is an apparatus for mixing at least two fluid streams, a first fluid stream and a second fluid stream, efficiently and with minimal pressure loss. The apparatus comprises a first supply conduit having a first supply conduit receiving end for receiving the first fluid. The apparatus further comprises a second supply conduit having a second supply conduit receiving end for receiving the second fluid. The apparatus further comprises a mixing chamber in fluid communication with the first and second supply conduits at first and second supply conduit discharge ends opposite the first and second supply conduit receiving ends. One of the first or second supply conduit discharge ends leads substantially tangentially into the mixing chamber and the other of the first or second supply conduit discharge ends leads substantially radially into the mixing chamber. The apparatus further comprises a mixing chamber outlet for discharging a mixed stream of the first and second fluids from the mixing chamber, the mixing chamber outlet in fluid communication with the central region of the mixing chamber.
In a more specific embodiment, the present invention is an apparatus as described in the first embodiment and further comprising a plurality of first fluid distribution conduits for distributing the first fluid stream, a plurality of second fluid distribution conduits for distributing the second fluid stream, and a plurality of supply conduits, each having a receiving end and a discharge end, the receiving ends in alternating fluid communication with the first and second fluid distribution conduits and the discharge ends leading alternately substantially tangentially and substantially radially into the mixing chamber.
In another specific embodiment, the present invention is an apparatus as described in the first embodiment and further comprising a plurality of second fluid distribution conduits for distributing the second fluid stream, a plurality of third fluid distribution conduits for distributing a third fluid stream, and a manifold having an inlet and an outlet, the manifold inlet in fluid communication with the second and third distribution conduits arranged in a repeating sequence, and the manifold outlet in fluid communication with the second supply conduit receiving end.
In another embodiment, the present invention is a layered assembly for mixing at least two fluids. The assembly comprises a substantially planar cover layer having external and internal faces and defining first and second feed channels for receiving first and second fluids into the assembly. The first and second feed channels extend from the external surface to the internal surface to form first and second inlet ports. The assembly further comprises a substantially planar mixing layer having an upper and a lower face, where the mixing layer upper face is sealingly disposed on the cover layer internal face to define a first supply channel having a first supply channel receiving end in fluid communication with the first feed channel and a first supply channel discharge end opposite the first supply channel receiving end. The cover and mixing layers further define a second supply channel having a second supply channel receiving end in fluid communication with the second feed channel and a second supply channel discharge end opposite the second supply channel receiving end. The cover and mixing layers further define a mixing chamber in fluid communication with the first and second supply channel discharge ends, where one of the first or second supply channel discharge ends leads substantially tangentially into the mixing chamber and the other of the first or second supply channel discharge ends leads substantially radially into the mixing chamber. The cover and mixing layers further define a mixing chamber outlet channel in fluid communication with the mixing chamber for discharging a mixed stream of the first and second fluids from the mixing chamber.
In another embodiment, the present invention is a layered assembly as defined above where the cover layer and mixing layer each comprise one or more plates in a fluid-tight stacked arrangement.
In yet another embodiment, the present invention is a process for mixing at least two fluid streams. The process comprises flowing a first fluid stream through a first feed channel and injecting the first fluid stream radially into a mixing chamber. The process further comprises flowing a second fluid stream through a second feed channel, injecting the second fluid stream tangentially into the mixing chamber to create a vortex, and withdrawing a stream of mixed first and second fluids from the central portion of the vortex.
These and other embodiments and objects will become clearer after the detailed description of the invention.